1. Field of the Invention
The present invention relates to a copolymer suitable for a film, a sheet or a pipe, a process for the production thereof, and a molded article thereof. More specifically, the present invention relates to a copolymer suitable for a substitute article of a polyvinyl chloride (for example, a film, a sheet or a pipe), a process for production thereof, and a molded article thereof.
2. Description of the Related Art
In general, an elastic recoverability, transparency and mechanical strength found in a polyvinyl chloride are required for a copolymer to be used as various films such as, for example, wrapping film. However, the polyvinyl chloride comes in question concerning environmental pollution because of the possibility of generation of harmful substances at incineration, etc. Various kind of polymers are presently considered as a replacement for the polyvinyl chloride, but it is the status quo that none of them have been obtained satisfactory from the viewpoints of viscoelastic properties and transparency.
In recent years, progress has occurred in the field of polymerization of olefins such as ethylene or propylene. Particularly, a polymer having characteristics different from conventional polymers can be produced and an extremely small amount of catalyst can produce a large amount of polymer, because of the use of a catalyst using a transition metal compound such as a so-called metallocene, a non-metallocene or the like.
An application of such a catalyst to the copolymerization of ethylene with an alkenyl aromatic hydrocarbon represented by styrene has been proposed. For example, a pseudo-random copolymer (a random copolymer wherein methine carbon atoms with which a phenyl group is bonded are mutually separated by 2 or more of methylene groups without fail) of ethylene with styrene obtained by using a so-called homogeneous Ziegler-Natta catalyst using a specific transition metal compound and an organoaluminum compound is described in Japanese Patent Publication No. 2623070. Said copolymer is excellent in viscoelastic properties and transparency, and is expected as a replacement for polyvinyl chloride. However, there have been problems in that it has low oil resistance and insufficient heat resistance. Further, the copolymer obtained by said production process happens to have a deterioration of transparency because of the formation of a syndiotactic polystyrene as a by-product.
The application of such metallocene catalysts to the copolymerization of ethylene with a cyclic olefin represented by norbornene has been proposed. For example, a process for copolymerizing norbornene with ethylene using isopropylidene (cyclopentadienyl)(fluorenyl)titanium dichloride in Japanese Patent Publication (Kokai) No. 02-173112 or (tert-butylamido)dimethyl (tetramethylcyclopentadienyl) silanetitanium dichloride in Japanese Patent Publication (Kokai) No. 05-194641 as a catalyst component is disclosed. The copolymers obtained by these processes have high oil resistance and are useful as a heat resistant resin because of an extremely high glass transition temperature, but is inferior in flexibility to a copolymer of ethylene with styrene. The present invention was performed under the above-mentioned circumstances.
An object of the present invention is to provide a transparent copolymer excellent in flexibility and heat resistance and that""s constitution does not containing a halogen, so as to not be questioned from the viewpoint of environmental pollution.
Another object of the present invention is to provide a process for producing said copolymer at an extremely high polymerization activity, and a molded article of said copolymer.
Other objects of the present invention will be apparent from the following description.
In order to attain the above-mentioned objects, the present inventors have extensively studied the production of a copolymer based on a process for production using a transition metal compound represented by a metallocene as a catalyst component, and have thereby completed the present invention.
The present invention relates to a copolymer of (a) ethylene and/or an xcex1-olefin and (b) a cyclic olefin with (c) an alkenyl aromatic hydrocarbon, wherein the content of said cyclic olefin is 0.01 to 66 mol %, the content of said alkenyl aromatic hydrocarbon is 3 to 99 mol%, and the content of the alkenyl aromatic hydrocarbon is more than a half of the content of the cyclic olefin (and the sum of ethylene and/or the xcex1-olefin, the cyclic olefin and the alkenyl aromatic hydrocarbon is 100 mol %).
Further, the present invention relates to a process for producing said copolymer which comprises copolymerizing ethylene and/or an xcex1-olefin and a cyclic olefin with an alkenyl aromatic hydrocarbon in the presence of a catalyst prepared from (A) and [(B) and/or (C)] described below; and a molded article of said copolymer.
(A): a transition metal complex represented by the following general formula [I], [II] or [III]: 
(wherein M1 indicates a transition metal atom of the Group IV of the Periodic Table of the Elements; A indicates an atom of the Group XVI of the Periodic Table of the Elements; J indicates an atom of the Group XIV of the Periodic Table of the Elements; Cp1 indicates a group having a cyclopentadiene type anion skeleton; each of X1, X2, R1, R2, R3, R4, R5 and R6 independently indicates a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an aryl group, a substituted silyl group, an alkoxy group, an aralkyloxy group, an aryloxy group or a di-substituted amino group; X1 indicates an atom of Group XVI of the Periodic Table of the Elements; R1, R2, R3, R4, R5 and R6 may be optionally combined with each other to form a ring; and in the general formula [II] or [III], two of M1, A, J, Cp1, X1, X2, X3, R1, R2, R3, R4, R5 and R6 may be respectively the same or different.),
(B): one or more aluminum compounds selected from the following (B1) to (B3);
(B1) an organoaluminum compound represented by the general formula E1aAlZ3xe2x88x92a,
(B2) a cyclic aluminoxane having a structure represented by the general formula {xe2x80x94Al(E2)xe2x80x94Oxe2x80x94}b, and
(B3) a linear aluminoxane having a structure represented by the general formula E3{xe2x80x94Al(E3)xe2x80x94Oxe2x80x94}cAlE32 
(wherein E1, E2 and E3 respectively represent a hydrocarbon group, all of E1, all of E2 and all of E1 may be the same or different; Z represents a hydrogen atom or a halogen atom, and all of Z may be the same or different; xe2x80x9caxe2x80x9d represents a number satisfying the expression 0 less than axe2x89xa63; xe2x80x9cbxe2x80x9d represents an integer of 2 or more and xe2x80x9ccxe2x80x9d represents an integer of 1 or more); and
(C): a boron compound of any one of the following (C1) to (C3);
(C1) a boron compound represented by the general formula BQ1Q2Q3,
(C2) a boron compound represented by the general formula G+(BQ1Q2Q3Q4)xe2x88x92, and
(C3) a boron compound represented by the general formula (Lxe2x80x94H)+(BQ1Q2Q3Q4)xe2x88x92
(wherein B represents a boron atom in the trivalent valence state; Q1 to Q4 may be the same or different and respectively represent a halogen atom, a hydrocarbon group, a halogenated hydrocarbon group, a substituted silyl group, an alkoxy group or a di-substituted amino group; G+ represents an inorganic or organic cation; L represents a neutral Lewis base; and (Lxe2x80x94H)+ represents a Brxc3x8nsted acid).